1. Field of the Invention
The present invention relates to a light-absorbent resin composition for laser welding that is used when a plastic member is joined by a laser welding method, to a light-absorbent resin molding, and to a method for manufacturing a light-absorbent resin molding. The present invention more specifically relates to a light-absorbent resin composition for laser welding that has thermal stability not found in the conventional organic-based light-absorbing agent, and that imparts transparency and light-transmitting properties to a plastic member after laser welding that could not be obtained using a conventional carbon-based light-absorbing agent, to a light-absorbent resin molding, and to a method for manufacturing a light-absorbent resin molding.
2. Description of the Related Art
Instances in which a laser welding method is used as a method for bonding a thermoplastic resin have increased in recent years. A reason for this is considered to be that the use of the laser welding method has advantages in that an easily stabilized bond that is free of vibration can be formed even in a member having a fine complex bond interface, weld flash and smoke do not occurs, the appearance of the bonded product is enhanced, and the degree of freedom in the design of the bonded part is increased.
In the laser welding method, one of the plastic members to be bonded is usually composed of a light-transmissive resin molding, and the other plastic member is composed of a light-absorbent resin molding that absorbs laser light and generates heat.
When a laser is radiated to this plastic member from the direction of the light-transmissive resin molding, the light-absorbent resin molding first melts, and then heat is transmitted from the periphery of the molten light-absorbent resin molding to the light-transmissive resin molding to cause melting, and bonding occurs.
An Nd: YAG laser having a wavelength of 1064 nm or a semiconductor laser having a wavelength of 800 to 1000 nm is mainly used as the laser light source, and a material that efficiently absorbs near-infrared wavelengths of 800 to 1200 nm is therefore used as the light-absorbent resin composition for laser welding.
Known resin compositions that are used as the abovementioned light-absorbent resin composition for laser welding are resin compositions that contain as organic compounds phthalocyanine-based compounds, cyanine-based compounds, aminium-based compounds, immonium-based compounds, squalium-based compounds, polymethine-based compounds, anthraquinone-based compounds, and azo-based compounds, or as inorganic compounds, carbon black (see Japanese Laid-open Patent Application No. 2004-148800).
In Japanese Laid-open Patent Application No. 2005-290087, a light-absorbent resin composition for laser welding is proposed in which copper phosphonate having an aromatic ring, and metallic elements, salts, oxides, hydroxides, and the like are added in order to enhance sensitivity to the laser. Specific examples of the metal oxides included in the proposed resin composition include silicon oxide, titanium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, cobalt oxide, lead oxide, tin oxide, antimony oxide, indium oxide, manganese oxide, molybdenum oxide, nickel oxide, copper oxide, palladium oxide, lanthanum oxide, antimony-doped tin oxide (ATO), indium-doped tin oxide (ITO), and the like.
In International Patent Publication WO 2005/084955 pamphlet A1, a light-absorbent resin composition for laser welding is proposed in which tin-doped indium oxide (ITO) and antimony-doped tin oxide (ATO) are added as inorganic-based materials having light absorbing capability in the laser wavelength region.